Problem: Simplify the following expression: $z = \dfrac{3}{2p} - \dfrac{1}{9p}$
Solution: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2p$ and $9p$ $\lcm(2p, 9p) = 18p$ $ z = \dfrac{9}{9} \cdot \dfrac{3}{2p} - \dfrac{2}{2} \cdot \dfrac{1}{9p} $ $z = \dfrac{27}{18p} - \dfrac{2}{18p}$ $z = \dfrac{27 -2}{18p}$ $z = \dfrac{25}{18p}$